This online Stoichiometry Calculator finds the stoichiometric coefficients to balance a given chemical equation and computes amounts of the reactants and products of the reaction, both in moles and grams. The equations may include free electrons and electrically charged molecules (ions) as well as hydrated compounds. In case the original equation was unbalanced, the field with this equation is highlighted in light pink.
You can enter a chemical equation manually or paste the equation copied from a web page or text document (including DOC or PDF file). Indices denoted using <sub> and </sub> html tags (e.g. H2O) as well as denoted using the ‘tiny’ numbers, like ₂ or ₅ , (e.g. H₂O) are supported and automatically converted to normal form. In a hydrated compound the middle dot (·) or the asterisk (*) precedes the water formula (e.g. CuSO4·5H2O). In what follows is a more detailed syntax guide to our calculator.
The reaction stoichiometry is calculated automatically for a balanced equation, with the number of moles for the compounds being the same as the stoichiometric coefficients. You can enter either the required number of moles or weight in grams for one of the compounds in the corresponding field, and then press the ‘Enter’ key, to compute new values for the rest of the compounds.
Stoichiometry Calculations
Stoichiometry is the field of chemistry that studies the relative amounts of reactants and products in chemical reactions. For any balanced chemical equation, whole numbers (stoichiometric coefficients) are used to show the amounts (in moles) of both the reactants and products. Knowing the molecular weight of the compounds involved in the reaction, it is easy to find the mass of these compounds in grams.
So, the first step in stoichiometry calculations is balancing chemical equations. This means looking for stoichiometric coefficients for the reactants and products. It’s important because in a chemical reaction, the quantity of each element does not change (the law of conservation of mass). Thus, each side of the equation must represent the same quantity of atoms of any chemical element. In case of ionic reactions, the same electric charge must be present on both sides of the equation.
There are a number of methods for balancing chemical equations. But in case of complex reactions involving many compounds, it is preferable to balance equations using algebraic methods, based on solving a set of linear equations.
Our stoichiometry calculator uses the Gauss-Jordan elimination algorithm for solving a set of linear equations. The method is modified for finding integer coefficients.
Syntax Guide
• Reactants and products in a chemical reaction are separated by an equal sign (=). The substances are separated by a plus sign (+).
• The formula of a substance should be entered using the upper case for the first character in the element’s name and the lower case for the second character (compare: Co – cobalt and CO – carbon monoxide).
• Indices should be entered as normal numbers after the appropriate elements or groups, e.g. H2O for a water molecule or (NH4)2SO4 for ammonium sulfate.
• Parentheses ( ), square brackets [ ] and braces (curly brackets) { } can be used in the formulas. Nested brackets are also allowed, e.g. [Co(NH3)6]Cl3. The degree of nesting is unlimited, but all the brackets should be balanced.
• In a hydrated compound the middle dot (·) or the asterisk (*) must go before the water molecule formula (e.g. CuSO4·5H2O).
• To denote an ion specify its charge in curly brackets after the compound: {+2} or {2+}. Example: H{+}+CO3{2-}=H2O+CO2.
• To include an electron into a chemical equation, use {-}, e.g. Fe{+3}+{-}=Fe.
• Do not enter the state of compounds such as solids (s), liquids (l) or gases (g).
Using Stoichiometry Calculator
When entering a chemical equation manually or pasting the copied equation, it converts automatically to the ‘normal’ form according to the above rules. All the spaces are ignored and symbol → is converted to =. But symbols ↑ and ↓ remain in place.
Note, that both indices and charges can be denoted in the source document using <sub></sub> and <sup></sup> html tags, e.g. SO4-2, or denoted using the ‘tiny’ symbols, e.g. SO₄⁻². They are also converted automatically to the ‘normal’ form.
A single electron can be denoted as e– (e<sup>-</sup>) or e⁻ (with ‘tiny’ minus).
Output format
Using the appropriate drop-down menu, one can choose an output format for the balanced chemical equation:
• Html – The balanced equation is represented using html tags for indices and charges. A single electron is denoted as e–. Clicking the ‘Copy to clipboard’ button ( ) you can copy the result ‘as is’, including all the tags, and then you can paste it into any html-page. However, clicking Ctrl-A and Ctrl-C you can copy the result without the tags and paste it into a DOC document keeping duly formatted indices and charges.
• Small indices – The balanced equation is represented using ‘tiny’ symbols for indices and charges. For example, CO₃²⁻ where Unicode characters are used: ₃ = (\u2083), ² = (\u00B2), ⁻ = (\u207B). A single electron is denoted as e⁻.
• Normal – The balanced equation is represented according to the above syntax guide.
Error notifications
There are a number of obvious notifications in case of error detected in the course of initial inspection of the entered equation, like Unexpected character or Brackets not balanced. The following notifications deserve special attention:
Improper equation – The entered equation has chemical elements on the left-hand side that are missing on its right-hand side, or vice versa.
Impossible reaction – The entered equation represents an impossible reaction. For example, the equation (NH4)2SO4=NH4OH+SO2 has only trivial solution when all the coefficients set to zero.
Multiple independent solutions – The entered equation can be balanced in an infinite number of ways. Usually it is a combination of a few different independent reactions. For example, the equation H+O=H2O+HO has no unique solution because, for instance, two solutions are 3H+2O=H2O+HO and 4H+3O=H2O+2HO which are not multiples of each other. The equation can be separated as H + O = H2O and H + O = HO, each of which does have a unique solution.
Element “…” doesn’t exist – An element’s name, entered in accordance with the above syntax guide, does not indicate a real chemical element. Sometimes an immutable group in chemical compounds is replaced with a fictitious element to balance the equation, which otherwise can not be uniquely balanced. In this case, our calculator will balance the chemical equation but will not compute the reaction stoichiometry.
Example of Stoichiometry Calculations
Consider the combustion of methyl mercaptan (CH4S or CH3SH) that produces sulfur dioxide:
and answer the following questions:
a) How many grams of sulfur dioxide (SO2) are formed from complete combustion of 4 g of CH4S ?
b) How many grams of SO2 are formed when 4 g of CH4S react with 3 g of O2 ?
With the help of our stoichiometry calculator, we can easily get the result in no time.
First, copy the above equation as it is and paste it into the ‘Equation to Balance’ field of the calculator. It immediately converts to the ‘normal’ form. Then click the ‘Calculate’ button. This field is now highlighted in light pink, indicating that the original equation was unbalanced. In the ‘Balanced Equation’ field you will have the result:
Below is the table of the reactants and products of the reaction with amounts for each compound. The number of moles for the compounds are indicated the same as the stoichiometric coefficients in the equation. The amount in grams for each compound is calculated to be a product of the compound molecular weight and the respective number of moles.
These fields are interactive, and you can change any amount value and all the other fields are automatically recalculated. So let’s get down to solving the above problems.
a) Enter 4 in the grams field for CH4S and press the keyboard ‘Enter’ key. You will immediately get 5.326725 g for SO2.
b) Note that complete combustion of 4 g of CH4S requires 7.981831 g of O2. So if only 3 g of O2 react with CH4S then oxygen is the limiting reactant. This means that we must enter 3 g for O2 and get that only 1.503415 g of CH4S will react to yield 2.002069 g of SO2.
Related calculators
Check out our other chemistry calculators such as Chemical Equation Balancer Calculator or Molecular Weight Calculator.